So, I am on my second D2G and my 5th MicroSD.
I can transfer music any way I want til about 3gb - once I hit that limit, the phone will lock up any music program and the micro SD will not stay mounted properly.
I have done everything from buying 2 other 8gb MicroSD cards (other than the 16gb class 10 I intend to use, both different brands from the 16 gb and each other - Kingmax, PNY, SanDisk), reformatting all 3 non-stock cards to various settings (including emulating the cluster size of the stock card that came with the phone). I have system restored and re-flashed the phone from an SBF file, tried other ROMs, etc.
The cards all check out 100% healthy in 2 different tests on PC and on the Mac disck utility and all work fine in my other android based phones. The stock card is the only one of the 4 total that works in the Droid 2 Global... Which baffles me and is the only reason I fear its not the phone.
On top of all the card tests, I have loaded music files to my cards via Airsync (Wifi), DoubleTwist (USB Connection), Direct dragging them to the mounted phone (USB Connection), and plugging the MicroSD into an adapter and directly copying over. This had been done mainly Mac, then the USB drag-n-drop and adapter drag-n-drop were done on a PC again (card formats and testing between to verify my Mac was not the culprit). All cards continued to test clean 100% working and all other Androids are happy with the cards.
The Droid 2 Global will still do the black screen thing once the phone has fully initialized the card(s). Once the screen "sleeps" it stays black, but a back light comes on like it tries when I try to resume it from sleep.